Construction of carbon nanotube-supported CuO–Fe3O4 dual-site catalysts for ambient electrosynthesis of ammonia

Abstract

The electrocatalytic nitrate (NO₃⁻) reduction reaction (NitRR) to ammonia (NH₃) is considered a sustainable and environmentally friendly approach for synthesizing ammonia. However, the electrocatalyst encounters challenges related to the limited distribution of NO₃⁻ and insufficient active hydrogen on the catalyst surface, which result from the high concentration of NO₃⁻ and the difficulty of water splitting under ambient conditions. Here, by introducing Cu and Fe oxides onto carbon nanotube substrates (CuO–Fe₃O₄/CNTs), a CuO–Fe₃O₄ dual-site synergistic catalytic mechanism is proposed to promote the adsorption and conversion of NO₃⁻ at Cu species sites and accelerate water splitting at Fe species sites, thereby significantly enhancing the performance of nitrate reduction reactions. The as-synthesized CuO–Fe₃O₄/CNTs exhibits good activity for the NitRR, achieving an NH₃ yield rate of 39.2 ± 3.5 mg h⁻¹ mg_cat.⁻¹ and a faradaic efficiency of 90.5 ± 2.2% at −0.8 V (vs. RHE). Furthermore, different in situ characterizations were employed to identify intermediates in the electrocatalytic NitRR process, confirming CuO–Fe₃O₄/CNTs as a promising catalyst for NH₃ electrosynthesis.